The present invention relates to redundant processors operating in parallel and particularly to processors which run synchronously in conjunction with the operation of an integrated telephone message accounting system (IMAS).
In prior telephone switching systems, redundant processors and self-checking techniques have been employed to prevent a single point failure which otherwise could cause the entire system to stop functioning. In such systems, faulty subsystems are automatically switched off-line to provide minimum interruption to service.
In one prior system, redundant processors each perform identical jobs and each compares the other's output. When a difference in output exists, each processor enters a diagnostic subroutine to determine which of the processors is defective. This prior system, however, requires positive synchronization between the processors. Also, that prior system requires considerable software dedicated to the diagnostic subroutine. The diagnostic subroutine undesirably requires large memory capacity and execution of the diagnostic subroutine impares the normal function of handling system traffic.
Another prior system employs two processors each with a self-test subroutine which is periodically run. In such a prior system, positive synchronization is desirably not required since only one processor is active and the other is standby. However, such a system has a problem in that single point failures are detected only with a software subroutine.
In view of the above background, there is a need for an improved processor configuration which economically eliminates processing stoppages due to single point failures, without introducing software burdens which degrade the real time performance of the normal system functions.